there are multiple models modelling aspects of climate, many of which individually need super computer levels of horsepower. So separate models for ocean heating, or air currents etc.

all of which would have to re-work to account for the new entropy being added to the system, and its intended effects.

And this gets further complicated by different methods to change the environment.

Unless a climate scientist corrects me, its not as simple as just plugging in a x=x-c.

And that adds more complexity to the model too, not to mention the change in all the data - before G-eng, after G-eng.